Universal I-Q relations for rapidly rotating neutron and strange stars in scalar-tensor theories

We study how rapid rotation influences the relation between the normalized moment of inertia $\bar{I}$ and quadrupole moment $\bar{Q}$ for scalarized neutron stars. The questions one has to answer are whether the EOS universality is preserved in this regime and what are the deviations from general relativity. Our results show that the $\bar{I}-\bar{Q}$ relation is nearly EOS independent for scalarized rapidly rotating stars, but the differences with pure Einstein's theory increase compared to the slowly rotating case. In general, smaller negative values of the scalar field coupling parameters $\beta$ lead to larger deviations, but these deviations are below the expected accuracy of the future astrophysical observations if one considers values of $\beta$ in agreement with the current observational constraint. An important remark is that although the normalized $\bar{I}-\bar{Q}$ relation is quite similar for scalar-tensor theories and general relativity, the unnormalized moment of inertia and quadrupole moment can be very different in the two theories. This demonstrates that although the $\bar{I}-\bar{Q}$ relations are potentially very useful for some purposes, they might not serve us well when trying to distinguish between different theories of gravity.Comment: 8 pages, 3 figure

Static and slowly rotating neutron stars in scalar-tensor theory with self-interacting massive scalar field

Binary pulsar observations and gravitational wave detections seriously constrained scalar-tensor theories with massless scalar field allowing only small deviations from general relativity. If we consider a nonzero mass of the scalar field, though, significant deviations from general relativity are allowed for values of the parameters that are in agreement with the observations. In the present paper we extend this idea and we study scalar-tensor theory with massive field with self-interaction term in the potential. The additional term suppresses the scalar field in the neutron star models in addition to the effect of the mass of the scalar field but still, large deviations from pure GR can be observed for values of the parameters that are in agreement with the observations.Comment: 9 pages, 5 figure

Multi-scalar Gauss-Bonnet gravity: scalarized black holes beyond spontaneous scalarization

Recently, a new nonlinear mechanism for black hole scalarization, different from the standard spontaneous scalarization, was demonstrated to exist for scalar Gauss-Bonnet theories in which no tachyonic instabilities can occur. Thus Schwarzschild black hole is linearly stable but instead nonlinear instability can kick-in. In the present paper we extend on this idea in the case of multi-scalar Gauss-Bonnet gravity with exponential coupling functions of third and fourth leading order in the scalar field. The main motivation comes from the fact that these theories admit hairy compact objects with zero scalar charge, thus zero scalar-dipole radiation, that automatically evades the binary pulsar constraints on the theory parameters. We demonstrate numerically the existence of scalarized black holes for both coupling functions and for all possible maximally symmetric scalar field target spaces. The thermodynamics and the stability of the obtained solution branches is also discussed.Comment: 12 pages, 4 figure

CFD – facilitated Prognosis of Bubble Bed Bioreactor Performance Based on Bubble Swarms Oscillation Analysis

Bubble column reactors are widely used as gas-liquid and gas liquid-solid contactors in biotechnology applications. A basic issue in biotechnology is oxygen availability related to gas hold-up distribution, since aerobic bioprocessing depends on the dissolved oxygen substrate. The aim of this study is to analyze oxygen availability in bubble column bioreactors in terms of specific spatial and temporal gas-liquid flow. 3D CFD simulation is used to simulate the dispersed gas-liquid flow field of a bubble column of ID 0.29 m equipped with metal distributing plate. The solution is based on the Euler/Euler approach, the standard k-ε model, and the standard wall function treatment. A single size particle model was employed. No mass transfer between the gas and the liquid phase was studied; oxygen transfer is discussed in terms of local and temporal gas hold-up distribution. Two cases of different viscosity are studied related to water-like and sugar-containing nutrient media cases, e.g. tap water and aqueous solution of 0.3 kg kg–1 saccharose, respectively. Conditions of oxygen availability for aerobic cell growth in a bio-fluid at condition of elevated viscosity are considered. The time-course of instantaneous oxygen delivery proportional to the dispersion capacity estimated as gas hold-up is uncovered. The results are presented in the form of contour plots and radial profiles of the local gas hold-up at different bed height positions. The oscillating behaviour of the gas hold-up is illustrated and summarized into oxygen availability plot related to position. Based on the CFD analysis, clues for rational bioprocess performance time-course could be inferred

CFD – facilitated Prognosis of Bubble Bed Bioreactor Performance Based on Bubble Swarms Oscillation Analysis

Bubble column reactors are widely used as gas-liquid and gas liquid-solid contactors in biotechnology applications. A basic issue in biotechnology is oxygen availability related to gas hold-up distribution, since aerobic bioprocessing depends on the dissolved oxygen substrate. The aim of this study is to analyze oxygen availability in bubble column bioreactors in terms of specific spatial and temporal gas-liquid flow. 3D CFD simulation is used to simulate the dispersed gas-liquid flow field of a bubble column of ID 0.29 m equipped with metal distributing plate. The solution is based on the Euler/Euler approach, the standard k-ε model, and the standard wall function treatment. A single size particle model was employed. No mass transfer between the gas and the liquid phase was studied; oxygen transfer is discussed in terms of local and temporal gas hold-up distribution. Two cases of different viscosity are studied related to water-like and sugar-containing nutrient media cases, e.g. tap water and aqueous solution of 0.3 kg kg–1 saccharose, respectively. Conditions of oxygen availability for aerobic cell growth in a bio-fluid at condition of elevated viscosity are considered. The time-course of instantaneous oxygen delivery proportional to the dispersion capacity estimated as gas hold-up is uncovered. The results are presented in the form of contour plots and radial profiles of the local gas hold-up at different bed height positions. The oscillating behaviour of the gas hold-up is illustrated and summarized into oxygen availability plot related to position. Based on the CFD analysis, clues for rational bioprocess performance time-course could be inferred